1. Field of the Invention
The present invention relates to a printer that supports a power save mode and that performs printing by accepting a print request from a client via a network. The invention also relates to a power save control method for the same.
2. Description of the Related Art
Generally, printers support a power save mode to save energy, and go into the power save mode when a prescribed condition occurs. Transitions between the power save mode and other modes are illustrated in FIG. 1. In the figure, standby mode is a state in which the printer is ready to print upon accepting a print request. On the other hand, the power save mode is a state in which the printer is put in an energy saving state; in this state, the printer can accept a print request, but cannot start printing at once because the process section, containing the paper transport unit, photoconductor, developing unit, charge unit, and transfer unit, as well as the fusing unit, is powered off and it takes time for the fusing unit, cooled down to normal temperature, to be heated up to its operating temperature. A warmup mode is a state in which the printer is performing initialization for printing such as preheating the fusing unit.
The following control is employed for causing a transition to the power save mode. In a first prior art, control is perform to automatically cause a transition to the power save mode when a prescribed time has elapsed from the last access. In a second prior art, working clients are examined by sending PING (Packet Internet Groper) packets, and the transition to the power save mode is controlled in accordance with the network condition (see Japanese Unexamined Patent Publication No. 2000-137550).
In the first prior art, the condition for transitioning to the power save mode is fixed, regardless of the external environment. That is, even when there are no working clients on the network, transition to the power save mode cannot be made until after a preset time has elapsed.
On the other hand, in the second prior art, while the network condition can be detected dynamically, and an optimum power save control can be performed based on the detected condition, the following problems remain to be solved.
(1) Wasteful packets flow through the network, resulting in increased traffic. If there are many printers on the network, and if the printers send PING packets to a large number of clients at predefined intervals of time, a considerable amount of traffic occurs.
(2) Sending a packet means providing some kind of information to other devices on the network. The amount of information contained in a PING packet is small, but since it at least has the function of telling other hosts that the sending device is working normally, the packet may affect other devices. In a simple example, when some other device is monitoring packets on the network to determine whether or not it should go into power save mode, there may arise the problem that the device cannot make a transition to the power save mode because of the PING packet.
(3) Since a response to the PING packet must be returned, it puts a burden on the receiving device.